The invention relates to the manufacture of fusion-cast refractories with cavities or hollow portions therein formed by cores disposed in molds employed in the fusion casting process. In particular, it relates to a new dynamic core apparatus and technique for improving the manufacture of such fusion-cast articles.
Exemplary general description of the manufacture of fusion-cast refractories is given in U.S. Pat. No. 1,615,750 and in the book entitled "Refractories" by F. H. Norton, 4th edition, published 1968 by McGraw-Hill Book Co., New York, on pages 186-9.
Heretofore, most efforts in forming cavities or hollow portions in fusion-cast articles have involved utilization of cores maintained in place until after the solidified casting had cooled through the annealing stage. Such stationary cores were commonly formed of various shaped and baked refractory grains. See U.S. Pat. Nos. 1,903,944, 2,023,044 and 2,071,542. These cores were supposedly designed to overcome the problem of the casting cracking as a result of the cooling shrinkage of such castings around and onto cores that were generally inflexible. Although they were successful in some cases, this cracking problem has persisted in a number of other cases for a variety of reasons (e.g. lack of core grains with appropriate characteristics vis a vis those of the cast molten refractory, size of cores and castings, etc.).
One earlier alternative solution to such continuing problem was the employment of a core made of metal that melted after an initial layer of solidified refractory formed on it and immediately allowing such melted core metal to flow out of the casting and mold via an aperture in the mold previously sealed by such core. See U.S. Pat. No. 2,004,378. Upon further cooling, the casting did not encounter resistance to its natural shrinkage and, accordingly, did not suffer the cracking associated with stationary cores of baked refractory grains or similar generally inflexible types. Nevertheless, this technique of the melting metal core suffers from the difficulty of not being able to economically or practically make the critical selection of a metal vis a vis the fusion-cast refractory such that the metal will not melt prematurely (to avoid "break-out" of molten refractory through a thin and weak solidified layer no longer supported by the core) and will melt rapidly enough at the necessary time (to avoid resistance by the core to shrinkage of the solidified casting portion therearound that leads to cracking of the casting).